pgsql: Stabilize stats_ext test with other collations

Stabilize stats_ext test with other collations

The tests used string concatenation to test statistics on expressions,
but that made the tests locale-dependent, e.g. because the ordering of
'11' and '1X' depends on the collation. This affected both the estimated
and actual row couts, breaking some of the tests.

Fixed by replacing the string concatenation with upper() function call,
so that the text values contain only digits.

Discussion: https://postgr.es/m/b650920b-2767-fbc3-c87a-cb8b5d693cbf%40enterprisedb.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/2a058e938c73bfb85bbc9fa93dea74788043ca6c

Modified Files
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src/test/regress/expected/stats_ext.out | 204 ++++++++++++++++----------------
src/test/regress/sql/stats_ext.sql      | 102 ++++++++--------
2 files changed, 153 insertions(+), 153 deletions(-)